Track circuit surge protection

ABSTRACT

A surge suppression circuit for a track circuit is provided. The surge suppression circuit comprises a first surge protection device including a first pair of silicon avalanche diodes and a second surge protection device including a second pair of silicon avalanche diodes. The first surge protection device is connected on a first connection line between a first terminal of a railroad signaling electronic equipment to be protected from a surge and a first terminal of a first rail of two physical rails. The second surge protection device is connected on a second connection line between a second terminal of the railroad signaling electronic equipment and a second terminal of a second rail of the two physical rails. The first surge protection device and the second surge protection device are connected to an earth ground terminal.

BACKGROUND 1. Field

Aspects of the present invention generally relate to surge protection ofa track circuit. Specifically, the present disclosure relates to animproved technology for track circuit surge protection, applicable forexample to grade crossing predictor (GCP) territory.

2. Description of the Related Art

The application of railroad signal wayside and crossing equipmentnecessitates that it is installed adjacent to the rails themselves. Infact, there is an electrical connection to the rails to facilitatesignal transfer in most situations. This situation covers a great numberof different systems.

Frequently the case, houses and appliances associated with the equipmentare the highest/tallest metal objects located in that area.Additionally, the rails themselves are grounded (earthed) as are theafore mentioned cases, houses, and appliances. Exposure to surges isfrom two sources: lightning and man-made.

Because of the distributed railroad environment and these specificfactors: tallest objects in area and connected to ground (earth) makethe railroad signal equipment a frequent target of lightning surgesdischarging to the ground. The lightning surges can be several millionvolts and thousands of amps which have the potential to catastrophicallydamage the rail signal equipment. There is only one other industry withsimilar exposure-aircraft.

Man-made surges are a result of “Power Transmission” problems andfaults. Although they do not contain the same peak energy thesesituations are more frequent and have a much longer duration thanlightning type events.

Understanding this; the industry established a methodology unique to theexposure conditions (much different than communications) toprotect/shield the rail signal equipment from damage by the lightningsurges and at the same time offer at least some protection from thePower Fault events. The techniques of shielding for tall structures andcables and suppression for the electromechanical and electronicequipment were the investigated methodologies. Shielding uses groundgrids, grounded wires and plates to allow the surge to conduct away fromthe protected wire. While the shielding process prevents some level ofdamage (especially power related) more was required in the suppressionarena. The first devices designed for surge suppression were air gaparrestors. Since the early equipment was relay/motor-based technology“air gap” devices were used initially to protect this equipment fromsurges.

Air Gap arrestors are constructed with two plates separated by severalthousandth's of an inch (the air gap). When the surge event happens, thecharge ionizes the air in the gap space. This ionized air passes thesurge current from on contact point to the other. Because on side istypically tied to earth ground this allows the surge current to flow toearth rather than through the protected equipment.

The “air gap” devices are very robust and reliable as a source ofprotection for the relay/motor devices and electronics. They were firstused in the 1930's and were designed by a Siemens predecessor companyand are still in use today.

In order to understand the performance of the arrestor one needs toconsider the surge environment they must protect against. Although aspreviously mentioned the initial surge event can be millions of voltsand thousands of amps. By the time the surge reaches the equipment to beprotected this has decreased to several thousand volts and severalthousand amps. The decrease is due to resistance in the air andconductors in the railroad system. Although values can be higher a surgeevent is characterized by less than 50,000 amps and most frequently inthe 20,000 amp area. For a 20 Ka waveform (8×20-ANSI/I.E.E.E.) the “gap”device will limit the voltage about 1,200 and current to 3,000 amps inabout 1 ms time.

As such the “Air Gap” device was perfect for motors and relays, but notquite adequate for pure electronic circuits which can be damaged by lessthan 100 volts, and in less time than an air gap provides protection.

Further studies were conducted in order to identify improved surgemitigation. This led to a layered protection technique which is stillused today (See AREMA Section 11). In addition to improved shieldingtechniques this technique typically has used “Air Gaps” as primary (HighLevel), Inductors, capacitors, and gas tube type devices as secondary(Mid Level), and solid state diodes, capacitors, resettable fuses astertiary level (Low Level).

Even with the layered methodology however the protection afforded wasnot completely reliable with today's microelectronics. As such changeshave been made along the way to improve the protection. Essentiallythese changes have involved solid state technology: Mov's, diodes, andgas tubes. Each of these devices is effectively an open circuit underambient conditions. As surge voltage builds the devices begin to conductcurrent until it reaches a short circuit state (quantum physics) andlimits the surge voltage and current. Typically, the voltage limit is afew hundred volts and current similar values. This process occurs inmicro seconds so it limits the surge event much faster than the Air Gapdevice.

While each of these has offered improvements there have always beenlimitations in amplitude handling ability and also concerns aboutfailure modes. The layered technique is still applied with thesolid-state devices. That has limited the application of the newtechnologies and in fact “Air Gaps” even with limitations are stillpopular.

Recent new surge arresting products introduced in the rail industryinclude improved gas tubes, MOV Gas Tube combinations and Zener diodes.Each of these devices offer better performance than air gaps both involtage clamping and current shunting to earth ground. These deviceshave provided enhanced protection when used in the conventional 3 deviceapplication—Line to Line and each line to earth ground. Although thesedevices are much faster to clamp there is still an overriding concernabout failure modes and using these devices in track circuitapplications.

Therefore, there is a need for providing a better surge suppression in atrack circuit.

SUMMARY

Briefly described, aspects of the present invention relate to a surgesuppression in a track circuit using a diode-based technology, i.e.,“silicon avalanche diodes (SADs)”. Recent advancements of thistechnology have become available which allow the proposed changes in thelayered methodology. The advantage of this technology is the speed inwhich it limits the surge. Initially this technology was applied withMOV's when used as a primary device. While this provided an improvedprotection level there was still “Failure Mode” concerns when applied totrack circuits. For this reason, they were used in limited applications.This technology shows not only significant improvements in voltage andcurrent limiting, but also because of construction minimizes the“Failure Mode” concerns as well. The key to this is the multilayeredconstruction of the SAD device.

In accordance with one illustrative embodiment of the present invention,a surge suppression circuit for a track circuit is provided. The surgesuppression circuit comprises a first surge protection device includinga first pair of silicon avalanche diodes and a second surge protectiondevice including a second pair of silicon avalanche diodes. The firstsurge protection device is connected on a first connection line betweena first terminal of a railroad signaling electronic equipment to beprotected from a surge and a first terminal of a first rail of twophysical rails. The second surge protection device is connected on asecond connection line between a second terminal of the railroadsignaling electronic equipment and a second terminal of a second rail ofthe two physical rails. The first surge protection device and the secondsurge protection device are connected to an earth ground terminal.

In accordance with another illustrative embodiment of the presentinvention, a method of providing a surge suppression in a track circuit.The method comprises providing a first surge protection device includinga first pair of silicon avalanche diodes and providing a second surgeprotection device including a second pair of silicon avalanche diodes.The first surge protection device is connected on a first connectionline between a first terminal of a railroad signaling electronicequipment to be protected from a surge and a first terminal of a firstrail of two physical rails. The second surge protection device isconnected on a second connection line between a second terminal of therailroad signaling electronic equipment and a second terminal of asecond rail of the two physical rails. The first surge protection deviceand the second surge protection device are connected to an earth groundterminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a surge suppression circuitincluding a first surge protection device and a second surge protectiondevice for providing surge protection to a track circuit in accordancewith an exemplary embodiment of the present invention.

FIG. 2 illustrates a track layout plan including first and secondarrestors for surge protection in accordance with an exemplaryembodiment of the present invention.

FIG. 3 illustrates a voltage waveform of an application with only twofirst and second arrestors but without an equalizer in accordance withan exemplary embodiment of the present invention.

FIG. 4 illustrates a front view of an arrestor in accordance with anexemplary embodiment of the present invention.

FIG. 5 illustrates a perspective view of an arrestor in accordance withan exemplary embodiment of the present invention.

FIG. 6 illustrates a front view of first and second arrestors inaccordance with an exemplary embodiment of the present invention.

FIG. 7 illustrates a view of silicon avalanche diode layers of a firstsurge protection device in accordance with an exemplary embodiment ofthe present invention.

FIG. 8 illustrates a schematic view of a flow chart of a method ofproviding a surge suppression in a track circuit in accordance with anexemplary embodiment of the present invention.

DETAILED DESCRIPTION

To facilitate an understanding of embodiments, principles, and featuresof the present invention, they are explained hereinafter with referenceto implementation in illustrative embodiments. In particular, they aredescribed in the context of an improved solution as a surge suppressioncircuit for a track circuit's surge protection. A multilayered design ofthe surge suppression circuit provides desired voltage/current clampingcharacteristics and the speed of same allow a major change in a primarylayer of protection. Embodiments of the present invention, however, arenot limited to use in the described devices or methods.

The components and materials described hereinafter as making up thevarious embodiments are intended to be illustrative and not restrictive.Many suitable components and materials that would perform the same or asimilar function as the materials described herein are intended to beembraced within the scope of embodiments of the present invention.

These and other embodiments of the surge suppression circuit accordingto the present disclosure are described below with reference to FIGS.1-8 herein. Like reference numerals used in the drawings identifysimilar or identical elements throughout the several views. The drawingsare not necessarily drawn to scale.

Consistent with one embodiment of the present invention, FIG. 1represents a block diagram of a surge suppression circuit 105 includinga first surge protection device 107(1) and a second surge protectiondevice 107(2) for providing surge protection to a track circuit 110 inaccordance with an exemplary embodiment of the present invention. Thesurge suppression circuit 105 for the track circuit 110 comprises thefirst surge protection device 107(1) including a first pair 112(1) offirst and second silicon avalanche diodes (SADs) 115(1-2). The surgesuppression circuit 105 further comprises the second surge protectiondevice 107(2) including a second pair 112(2) of first and second siliconavalanche diodes (SADs) 115(3-4). A surge protection device (SPD) 107 isa device that attenuates (reduces in magnitude) random, high energy,short duration over voltages caused by lightning, utilities, switching,etc. Such anomalies occur in the form of voltage and current spikes witha duration of less than half an ac voltage cycle. These high energypower spikes can damage railroad electronic equipment. A SurgeProtective Device (SPD) 107 or surge suppressors divert high energypower away from a load by providing a lower impedance path to commonpoint earth ground, i.e., a ground terminal (GND) 130.

The first surge protection device 107(1) is connected on a firstconnection line 117(1) between a first terminal 120(1) of a railroadsignaling electronic equipment 122 to be protected from a surge and afirst terminal 125(1) of a first rail 127(1) of two physical rails. Thesecond surge protection device 107(1) is connected on a secondconnection line 117(2) between a second terminal 120(2) of the railroadsignaling electronic equipment 122 and a second terminal 125(2) of asecond rail 127(2) of the two physical rails. The first surge protectiondevice 107(1) and the second surge protection device 107(2) areconnected to the ground terminal (GND) 130.

According to one embodiment, the first surge protection device 107(1) isa multilayered device that stacks the first pair 112(1) of the first andsecond silicon avalanche diodes (SADs) 115(1-2) together to reach adesired trigger level. Likewise, the second surge protection device107(2) is a multilayered device that stacks the second pair 112(2) ofthe first and second silicon avalanche diodes (SADs) 115(3-4) togetherto reach a desired trigger level. Because of its layered construction,the surge suppression circuit 105 substantially eliminates a risk of afailure mode problem on a track or it minimizes the “Failure Mode”concerns. The layering of the first pair 112(1) of the first and secondsilicon avalanche diodes (SADs) 115(1-2) or the second pair 112(2) ofthe first and second silicon avalanche diodes (SADs) 115(3-4)establishes an actual breakdown voltage such that each layer has anavalanche level of about 25 volts yielding a net breakdown voltage ofabout 200 volts.

The SAD devices 115 are a diode (made from silicon) that is designed toexperience avalanche breakdown at a specified reverse bias voltage. Thejunction of an avalanche diode 115 is designed to prevent currentconcentration and resulting hot spots, so that the diode 115 isundamaged by the breakdown. The avalanche breakdown is due to minoritycarriers accelerated enough to create ionization in the crystal lattice,producing more carriers which in turn create more ionization. Becausethe avalanche breakdown is uniform across the whole junction, thebreakdown voltage is nearly constant with changing current when comparedto a non-avalanche diode. Avalanche diodes 115 are optimized foravalanche effect, so they exhibit small but significant voltage dropunder breakdown conditions. This feature provides better surgeprotection. Avalanche diodes 115 have a small positive temperaturecoefficient of voltage.

The SAD devices 115 have an application to protect electronic circuitsagainst damaging high voltages. The avalanche diode 115 is connected tothe track circuit 110 so that it is reverse-biased. In other words, itscathode is positive with respect to its anode. In this configuration,the diode 115 is non-conducting and does not interfere with the trackcircuit 110. If the voltage increases beyond the design limit, the diode115 goes into avalanche breakdown, causing the harmful voltage to beconducted to ground. When used in this fashion, they are often referredto as clamping diodes or transient voltage suppressors because they fixor “clamp” the maximum voltage to a predetermined level. A clampingvoltage, also referred to as peak let through or suppressed voltagerating, is the amount of voltage the surge suppression circuit 105permits to pass through it to the attached load during a transientevent. The clamping voltage is a performance measurement of a surgesuppressor's ability to attenuate a transient.

In operation, any failure of a single diode 115 does not directly affectthe surge suppression circuit 105 since it triggers a fuse operationwithin a surge protection device 107 of the first surge protectiondevice 107(1) and the second surge protection device 107(2) which opensthe surge suppression circuit 105. The voltage/current clampingcharacteristics and a speed of operation of the surge suppressioncircuit 105 enable an enhanced level of a primary layer of protection.The first pair 112(1) of the first and second silicon avalanche diodes(SADs) 115(1-2) or the second pair 112(2) of the first and secondsilicon avalanche diodes (SADs) 115(3-4) act in concert to provide avoltage clamping action which transfers a surge current from a line117(1-2) to the earth ground, i.e., the ground terminal (GND) 130. Asurge current capacity is the maximum amount of surge current that thesurge suppression circuit 105 can pass for a single transient event.This level is used to indicate the protection capacity of a particularsurge suppressor design, and when specifying surge suppressors.

Each silicon avalanche diode of the first pair 112(1) of the first andsecond silicon avalanche diodes (SADs) 115(1-2) or the second pair112(2) of the first and second silicon avalanche diodes (SADs) 115(3-4)is applied in a reverse bias manner such that a cathode (C) 132 isconnected to a line 117(1-2) and an anode (A) 135 is connected to anearth ground, i.e., the ground terminal (GND) 130 and is configured tobreakdown at a specific voltage causing a surge current to avalancheconduct to the earth ground, i.e., the ground terminal (GND) 130. Anavalanche breakdown results in carriers (electrons) being acceleratedacross a diode junction 140 causing ionization within a silicon crystallattice of each silicon avalanche diode 115. During a surge event 142,an avalanche event 145 is uniform across the diode junction 140 whichprovides a consistent breakdown voltage regardless of a current level.

The “Advanced Silicon Avalanche Diode” Device has a much faster andprecise turn on point and shorter dissipation time which better protectsTrack Circuit Devices such as Grade Crossing Predictors (GCPs). Becausethe turn on speed and clamping times are so precise one of the typicalthree surge devices used for, i.e., the track (equalizer) is no longerrequired. The surge suppression circuit 105 has a lower clamping voltageand a faster dissipation of surge. It provides increased long-termreliability of track circuit equipment, reduced installation costs sincefewer devices are required, and less space is required in house.

Less energy is applied to equipment with a two-arrestor deviceconfiguration. The “Line to Line” device, the equalizer can beeliminated when using the arrestors using a diode-based technology,i.e., “silicon avalanche diodes (SADs)”. This largely eliminates therisk of “Failure Mode” problems on the track but provides a significantcost savings (requires 2 devices vs. 3 today). With this as a bonus lessspace/wiring is required as well. Within a typical installation thespace and cost savings will be significant.

The multilayered construction actually stacks several silicon avalanchediodes 115 together to reach a desired trigger level. Because the designis layered any failure of a single diode 115 does not directly affectthe track circuit 110 and in most cases trigger the “fuse operation”within the device (opens the circuit). Silicon Avalanche Diode (SAD)devices 115 show performance on the order of 10 times better than an airgap unit. Voltages were limited to less than 200 volts and time to clampwas less 50 microseconds. More than that, however, is the repeatabilityof this performance. The SAD devices 115 do not offer varied performanceas an air gap device. Air gaps clamping voltage will change (increase)over time due to temperature and moisture content of the air. Thevoltage will also increase as the metal plates are melted away by surgeevents. None of these limitations apply to the SAD devices 115. The useof these surge protection devices 107 using “Advanced Silicon AvalancheDiode” technology will greatly improve reliability of track circuitequipment.

Referring to FIG. 2 , it illustrates a track layout plan 200 includingfirst and second arrestors or surge protection devices 205(1-2) forsurge protection in accordance with an exemplary embodiment of thepresent invention. FIG. 2 is a section of an actual railroad signalplan. It shows the connection between an electronic control equipment207 and two physical rails of a track 210. The rail connections to thetrack 210 are labeled as “ETRB and ETRN”. The symbol #6 is for theselines to indicate the wire size going to the rails. The two symbolslabeled “H” are the first and second arrestors 205(1-2) which areapplied in this instance per the application. They are connected betweenthe lines ETRB and ETRN and an “earth ground (GND)” 215. To the right offirst and second arrestors 205(1-2) are 4 terminals (circles) labeledTB, RB, TN, RN with triangle symbols between a pair of the terminals.These symbols 1G18 and 1G16 are test terminals that allow the line to beopened electrically to allow for testing and measurements. Theelectronic control equipment 207 to protect is shown on the right sideof the figure and labeled “TIP-2 #1. It has 2 track connections labeledas “Track 1+ and Track 1−”. The #10 symbol represents the wire size forthese connections.

Turning now to FIG. 3 , it illustrates a voltage waveform 305 of anapplication with only two first and second arrestors or surge protectiondevices 205(1-2) of FIG. 2 but without an air gap equalizer inaccordance with an exemplary embodiment of the present invention. Theair gap equalizer is normally provided a “Line to Line” device betweentwo air gap arrestors such as the first and second arrestors 205(1-2) ofFIG. 2 . However, the “Line to Line” device, i.e., the equalizer iseliminated when using the two arrestors 205(1-2) using a diode-basedtechnology, i.e., “silicon avalanche diodes (SADs)”. This is so becausethe turn on speed and clamping times are so precise one of the typicalthree surge devices used for, i.e., the track (equalizer) is no longerrequired. The voltage waveform 305 shows Vmax=170V, Energy=24 mJ.

FIG. 4 illustrates a front view of an arrestor or a surge protectiondevice 400 in accordance with an exemplary embodiment of the presentinvention. The arrestor 400 comprises a housing 405 and two metalconnectors 410(1-2) coupled to a printed circuit board (PCB) 415 whichhas first and second surge protection devices 420(1-2) mounted on it.

As seen in FIG. 5 , it illustrates a perspective view of an arrestor ora surge protection device 500 in accordance with an exemplary embodimentof the present invention. The arrestor 500 comprises a printed circuitboard (PCB) 505 which includes a first pair of first and second siliconavalanche diodes (SADs) 515(1-2).

As shown in FIG. 6 , it shows a front view of first and second arrestorsor surge protection devices 600(1-2) in accordance with an exemplaryembodiment of the present invention. The arrestor 600(1) comprises aprinted circuit board (PCB) 605(1) which includes a first pair of firstand second silicon avalanche diodes (SADs) 615(1-2). The arrestor 600(2)comprises a printed circuit board (PCB) 605(2) which includes a secondpair of first and second silicon avalanche diodes (SADs) 615(3-4).

In FIG. 7 , it depicts a view of silicon avalanche diode layers 700 of afirst surge protection device 705 in accordance with an exemplaryembodiment of the present invention. An avalanche diode is a specialtype of semiconductor device designed to operate in reverse breakdownregion. Avalanche diodes are generally made from silicon or othersemiconductor materials. The construction of avalanche diode is similarto Zener diode but the doping level in avalanche diode differs fromZener diode. avalanche diodes are lightly doped. Therefore, the width ofdepletion layer in avalanche diode is very wide compared to the Zenerdiode. Because of this wide depletion region, reverse breakdown occursat higher voltages in avalanche diode. The breakdown voltage ofavalanche diode is carefully set by controlling the doping level duringmanufacture.

A normal p-n junction diode allows electric current only in forwarddirection whereas an avalanche diode allows electric current in bothforward and reverse directions. However, avalanche diode is specificallydesigned to operate in reverse biased condition. Avalanche diode allowselectric current in reverse direction when reverse bias voltage exceedsthe breakdown voltage. The point or voltage at which electric currentincreases suddenly is called breakdown voltage.

When the reverse bias voltage applied to the avalanche diode exceeds thebreakdown voltage, a junction breakdown occurs. This junction breakdownis called avalanche breakdown. When forward bias voltage is applied tothe avalanche diode, it works like a normal p-n junction diode byallowing electric current through it. When reverse bias voltage isapplied to the avalanche diode, the free electrons (majority carriers)in the n-type semiconductor and the holes (majority carriers) in thep-type semiconductor are moved away from the junction. As a result, thewidth of depletion region increases. Therefore, the majority carrierswill not carry electric current. However, the minority carriers (freeelectrons in p-type and holes in n-type) experience a repulsive forcefrom external voltage.

As a result, the minority carriers flow from p-type to n-type and n-typeto p-type by carrying the electric current. However, electric currentcarried by minority carriers is very small. This small electric currentcarried by minority carriers is called reverse leakage current. If thereverse bias voltage applied to the avalanche diode is furtherincreased, the minority carriers (free electrons or holes) will gainlarge amount of energy and accelerated to greater velocities. The freeelectrons moving at high speed will collide with the atoms and transfertheir energy to the valence electrons.

The valance electrons which gains enough energy from the high-speedelectrons will be detached from the parent atom and become freeelectrons. These free electrons are again accelerated. When these freeelectrons again collide with other atoms, they knock off more electrons.Because of this continuous collision with the atoms, a large number ofminority carriers (free electrons or holes) are generated. These largenumbers of free electrons carry excess current in the diode.

When the reverse voltage applied to the avalanche diode continuouslyincreases, at some point the junction breakdown or avalanche breakdownoccurs. At this point, a small increase in voltage will suddenlyincreases the electric current. This sudden increase of electric currentmay permanently destroy the normal p-n junction diode. However,avalanche diodes may not be destroyed because they are carefullydesigned to operate in avalanche breakdown region. The breakdown voltageof the avalanche diode depends on the doping density. Increasing thedoping density will decreases the breakdown voltage of the avalanchediode.

With regard to FIG. 8 , it illustrates a schematic view of a flow chartof a method 800 of providing a surge suppression in the track circuit110 in accordance with an exemplary embodiment of the present invention.Reference is made to the elements and features described in FIGS. 1-7 .It should be appreciated that some steps are not required to beperformed in any particular order, and that some steps are optional.

The method 800 in step 805 provides a surge suppression in the trackcircuit 110 by providing a first surge protection device including afirst pair of silicon avalanche diodes. The method 800 in step 810further provides a second surge protection device including a secondpair of silicon avalanche diodes. The first surge protection device isconnected on a first connection line between a first terminal of arailroad signaling electronic equipment to be protected from a surge anda first terminal of a first track of two physical rails. The secondsurge protection device is connected on a second connection line betweena second terminal of the railroad signaling electronic equipment and asecond terminal of a second track of the two physical rails. The firstsurge protection device and the second surge protection device areconnected to an earth ground terminal.

While a surge protection device including a pair of silicon avalanchediodes is described here a range of one or more other combination ornumber of diodes are also contemplated by the present invention. Forexample, other types of surge protection devices may be implementedbased on one or more features presented above without deviating from thespirit of the present invention.

The techniques described herein can be particularly useful for siliconavalanche diode (SAD) layers. The key to the present invention is amultilayered construction of a SAD device. A multilayered surgeprotection device stacks a pair of first and second silicon avalanchediodes (SADs) together. While particular embodiments of a surgeprotection device are described in terms of layers of two siliconavalanche diodes (SADs), the techniques described herein are not limitedto such two-layer design but can also be used with other latticestructures or configurations.

While embodiments of the present invention have been disclosed inexemplary forms, it will be apparent to those skilled in the art thatmany modifications, additions, and deletions can be made therein withoutdeparting from the spirit and scope of the invention and itsequivalents, as set forth in the following claims.

Embodiments and the various features and advantageous details thereofare explained more fully with reference to the non-limiting embodimentsthat are illustrated in the accompanying drawings and detailed in thefollowing description. Descriptions of well-known starting materials,processing techniques, components and equipment are omitted so as not tounnecessarily obscure embodiments in detail. It should be understood,however, that the detailed description and the specific examples, whileindicating preferred embodiments, are given by way of illustration onlyand not by way of limitation. Various substitutions, modifications,additions and/or rearrangements within the spirit and/or scope of theunderlying inventive concept will become apparent to those skilled inthe art from this disclosure.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, article, orapparatus.

Additionally, any examples or illustrations given herein are not to beregarded in any way as restrictions on, limits to, or expressdefinitions of, any term or terms with which they are utilized. Instead,these examples or illustrations are to be regarded as being describedwith respect to one particular embodiment and as illustrative only.Those of ordinary skill in the art will appreciate that any term orterms with which these examples or illustrations are utilized willencompass other embodiments which may or may not be given therewith orelsewhere in the specification and all such embodiments are intended tobe included within the scope of that term or terms.

In the foregoing specification, the invention has been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention. Accordingly, thespecification and figures are to be regarded in an illustrative ratherthan a restrictive sense, and all such modifications are intended to beincluded within the scope of invention.

Although the invention has been described with respect to specificembodiments thereof, these embodiments are merely illustrative, and notrestrictive of the invention. The description herein of illustratedembodiments of the invention is not intended to be exhaustive or tolimit the invention to the precise forms disclosed herein (and inparticular, the inclusion of any particular embodiment, feature orfunction is not intended to limit the scope of the invention to suchembodiment, feature or function). Rather, the description is intended todescribe illustrative embodiments, features and functions in order toprovide a person of ordinary skill in the art context to understand theinvention without limiting the invention to any particularly describedembodiment, feature or function. While specific embodiments of, andexamples for, the invention are described herein for illustrativepurposes only, various equivalent modifications are possible within thespirit and scope of the invention, as those skilled in the relevant artwill recognize and appreciate. As indicated, these modifications may bemade to the invention in light of the foregoing description ofillustrated embodiments of the invention and are to be included withinthe spirit and scope of the invention. Thus, while the invention hasbeen described herein with reference to particular embodiments thereof,a latitude of modification, various changes and substitutions areintended in the foregoing disclosures, and it will be appreciated thatin some instances some features of embodiments of the invention will beemployed without a corresponding use of other features without departingfrom the scope and spirit of the invention as set forth. Therefore, manymodifications may be made to adapt a particular situation or material tothe essential scope and spirit of the invention.

Respective appearances of the phrases “in one embodiment,” “in anembodiment,” or “in a specific embodiment” or similar terminology invarious places throughout this specification are not necessarilyreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics of any particular embodiment may becombined in any suitable manner with one or more other embodiments. Itis to be understood that other variations and modifications of theembodiments described and illustrated herein are possible in light ofthe teachings herein and are to be considered as part of the spirit andscope of the invention.

In the description herein, numerous specific details are provided, suchas examples of components and/or methods, to provide a thoroughunderstanding of embodiments of the invention. One skilled in therelevant art will recognize, however, that an embodiment may be able tobe practiced without one or more of the specific details, or with otherapparatus, systems, assemblies, methods, components, materials, parts,and/or the like. In other instances, well-known structures, components,systems, materials, or operations are not specifically shown ordescribed in detail to avoid obscuring aspects of embodiments of theinvention. While the invention may be illustrated by using a particularembodiment, this is not and does not limit the invention to anyparticular embodiment and a person of ordinary skill in the art willrecognize that additional embodiments are readily understandable and area part of this invention.

It will also be appreciated that one or more of the elements depicted inthe drawings/figures can also be implemented in a more separated orintegrated manner, or even removed or rendered as inoperable in certaincases, as is useful in accordance with a particular application.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any component(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or component.

What is claimed is:
 1. A surge suppression circuit for a track circuit,comprising: a first surge protection device including a first pair ofsilicon avalanche diodes; and a second surge protection device includinga second pair of silicon avalanche diodes, wherein the first surgeprotection device is connected on a first connection line between afirst terminal of a railroad signaling electronic equipment to beprotected from a surge and a first terminal of a first rail of twophysical rails, wherein the second surge protection device is connectedon a second connection line between a second terminal of the railroadsignaling electronic equipment and a second terminal of a second rail ofthe two physical rails, wherein the first surge protection device andthe second surge protection device are connected to an earth groundterminal, and wherein layering of the first pair of silicon avalanchediodes or the second pair of silicon avalanche diodes establishes anactual breakdown voltage such that each layer has an avalanche level ofabout 25 volts yielding a net breakdown voltage of about 200 volts. 2.The surge suppression circuit of claim 1, wherein the first surgeprotection device is a multilayered device that stacks the first pair ofsilicon avalanche diodes together to reach a desired trigger level. 3.The surge suppression circuit of claim 2, wherein any failure of asingle diode does not directly affect the track circuit since ittriggers a fuse operation within a surge protection device of the firstsurge protection device and the second surge protection device whichopens the surge suppression circuit.
 4. The surge suppression circuit ofclaim 1, wherein voltage/current clamping characteristics and a speed ofoperation of the surge suppression circuit enable an enhanced level of aprimary layer of protection.
 5. The surge suppression circuit of claim1, wherein the surge suppression circuit substantially eliminates a riskof a failure mode problem on a track.
 6. The surge suppression circuitof claim 1, wherein the first pair of silicon avalanche diodes or thesecond pair of silicon avalanche diodes act in concert to provide avoltage clamping action which transfers a surge current from a line toan earth ground.
 7. The surge suppression circuit of claim 1, whereineach silicon avalanche diode of the first pair of silicon avalanchediodes or the second pair of silicon avalanche diodes is applied in areverse bias manner such that a cathode is connected to a line and ananode is connected to an earth ground and is configured to breakdown ata specific voltage causing a surge current to avalanche conduct to theearth ground.
 8. The surge suppression circuit of claim 7, wherein anavalanche breakdown results in carriers (electrons) being acceleratedacross a diode junction causing ionization within a silicon crystallattice of the each silicon avalanche diode.
 9. The surge suppressioncircuit of claim 8, wherein during a surge event an avalanche event isuniform across the diode junction which provides a consistent breakdownvoltage regardless of a current level.
 10. A method of providing a surgesuppression in a track circuit, the method comprising: providing a firstsurge protection device including a first pair of silicon avalanchediodes; and providing a second surge protection device including asecond pair of silicon avalanche diodes, wherein the first surgeprotection device is connected on a first connection line between afirst terminal of a railroad signaling electronic equipment to beprotected from a surge and a first terminal of a first rail of twophysical rails, wherein the second surge protection device is connectedon a second connection line between a second terminal of the railroadsignaling electronic equipment and a second terminal of a second rail ofthe two physical rails, wherein the first surge protection device andthe second surge protection device are connected to an earth groundterminal, and wherein layering of the first pair of silicon avalanchediodes or the second pair of silicon avalanche diodes establishes anactual breakdown voltage such that each layer has an avalanche level ofabout 25 volts yielding a net breakdown voltage of about 200 volts. 11.The method of claim 10, wherein the first surge protection device is amultilayered device that stacks the first pair of silicon avalanchediodes together to reach a desired trigger level.
 12. The method ofclaim 10, wherein any failure of a single diode does not directly affectthe track circuit since it triggers a fuse operation within a surgeprotection device of the first surge protection device and the secondsurge protection device which opens the surge suppression circuit. 13.The method of claim 10, wherein voltage/current clamping characteristicsand a speed of operation of the surge suppression circuit enable anenhanced level of a primary layer of protection.
 14. The method of claim10, wherein the surge suppression circuit substantially eliminates arisk of a failure mode problem on a track.
 15. The method of claim 10,wherein the first pair of silicon avalanche diodes or the second pair ofsilicon avalanche diodes act in concert to provide a voltage clampingaction which transfers a surge current from a line to an earth ground.16. The method of claim 10, wherein each silicon avalanche diode of thefirst pair of silicon avalanche diodes or the second pair of siliconavalanche diodes is applied in a reverse bias manner such that a cathodeis connected to a line and an anode is connected to an earth ground andis configured to breakdown at a specific voltage causing a surge currentto avalanche conduct to the earth ground.
 17. The method of claim 16,wherein an avalanche breakdown results in carriers (electrons) beingaccelerated across a diode junction causing ionization within a siliconcrystal lattice of the each silicon avalanche diode.
 18. The method ofclaim 17, wherein during a surge event an avalanche event is uniformacross the diode junction which provides a consistent breakdown voltageregardless of a current level.